Complete spontaneous regression of metastatic merkel cell carcinoma: a case report and review of the literature.

Merkel cell carcinoma (MCC) is a rare aggressive primary cutaneous neuroendocrine neoplasm with a high rate of recurrence and metastasis. We report a case of a 94-year-old woman who experienced complete spontaneous regression of metastatic MCC. Nine months after complete excision of the primary MCC on her left eyebrow, metastatic MCC was confirmed with a fine-needle aspiration of a 4-cm mass on the left side of her neck. Three months later the mass had reduced in size to 2 cm and a neck dissection was performed. Her submandibular gland, thoracic duct and 25 lymph nodes were negative for MCC. Two of the lymph nodes, the larger measuring 1.3 cm, contained extensive amounts of fibrosis, with accumulation of macrophages and other chronic inflammatory cells. The literature documents 6 similar cases of complete spontaneous regression of metastatic MCC. The mechanism for regression is not well understood and is thought to involve T-cell-mediated immune response and apoptosis.